The cabling systems to which the invention applies include particularly, but not exclusively, cabling systems for aircraft, e.g. cabling systems that convey both the electrical power needed for powering on-board electrical loads and also signals for communication by networks. The invention also applies to cabling systems that convey only power.
The cables of interest may be cables made of copper, or aluminum, which may be shielded or not shielded, and which are connected together in bundles that are uniform or non-uniform, i.e. bundles of cables that are identical, similar, or different, and that run in parallel, being assembled together using collars or fasteners, e.g. arranged every 5 centimeters (cm).
When designing and using cable bundles, it is appropriate to pay attention to the thermal stresses to which the cables will be subjected. In particular, it is common practice to set a maximum heating limit (power given off by the Joule effect) for cables, so as to limit Joule effect losses, and also to set a maximum temperature and/or heating limit so that human maintenance operators are not in danger of being burnt when acting on the cables and so that the cables and their environments are not damaged.
In order to design and use such bundles, for cables that transfer electrical power, it is also appropriate to take account of the voltage drop that is authorized between the load and the power supply, as a function of the type of power supply network, e.g. a 28 volt direct current (DC28) network, or a 115 volt or 230 volt alternating current (AC115 or AC230) network. The maximum power feed to the cable and its electrical resistance, optionally after temperature correction, are considered by taking account, if there is correction, of the above-mentioned maximum temperature, which constitutes a conservative approximation that is very far removed from an optimum calculation. Conversely, if there is no correction, the results obtained are also very far from reality. Finally, it is appropriate to take account of the ability to withstand mechanical tension, so as to avoid damage by pulling out and partial or total breaking associated with the mechanical forces that might be applied to the cable. This aspect of design is governed by empirical rules that are not addressed herein.
The present disclosure seeks to improve how thermal constraints and voltage drops are taken into account. It seeks to provide an improvement in a field where reasoning is often applied by assuming that bundles are uniform, without taking account of the non-uniformity of the cables present therein, and in particular while taking into consideration only a single level of electrical loading of the cables, without specifying whether the cables rise in temperature or not, even though a power cable and a network communication cable do not heat up in the same way. This single loading level is selected by considering a single configuration of the system, e.g. an airplane, typically by considering that all of the equipment is operating at the same time, that pressure is at a minimum, and that temperatures are at their maximums. Naturally, such assumptions are excessively conservative, since certain pieces of equipment, such as landing gear actuators, are active for only a few seconds in any one flight. Furthermore, proceeding in that way amounts to imposing constraints that are incompatible since, for example, the main and emergency power supply circuits for a given piece of equipment are never powered simultaneously, or for example the maximum temperature is never reached at the same time as the minimum pressure.
In practice, those prior methods are based on very general calculation charts and involve calculating the temperature of each cable, and then comparing the temperatures as calculated in this way with the maximum allowable temperature. Very large safety margins are used since the calculations are performed cable by cable without taking account of the structure of the bundle, and also because the charts that are used are very conservative because of their general nature.
A method that is more expensive in terms of computation is known as the multi-physical method since it involves simulation that is complete, both electrically and thermally. This involves calculations involving time, with integrations to simulate transient stages in order to calculate the temperatures of each of the cables in each branch of the bundle corresponding to respective zones of the airplane and to calculate the diameters that are to be given to those cables. The temperature that is reached is compared with the maximum allowable temperature.
Such a calculation makes it possible to reduce the margin used when dimensioning cables and bundles, but it is cumbersome and impractical for systems involving numerous cables or electrical connections that are too complex, as applies for cabling in airplanes, since it implies that a model needs to be generated beforehand for each system under study, the model needs to be opened each time modeling is performed, parameters are modified, the simulation is executed, the results are collected, and the model is closed, which is highly constraining.